Two-stage anoxic-oxic (A/O) system for the treatment of coking wastewater: Full-scale performance and microbial community analysis

Coking wastewater (CWW) is one of the most challenging industrial wastewaters to treat, due to its complex chemical composition, high organic load, and potential toxicity to human and environmental health. A full-scale coking wastewater treatment plant with a two-stage anoxic-oxic-anoxic-oxic (A1/O1/A2/O2) process was investigated systematically. The experimental results showed that the AOAO process exhibited an excellent removal capacity of COD, ammonia, nitrate, and total nitrogen. The GC × GC-TOF MS analysis investigated that the majority of refractory organic compounds, such as phenols, quinolines, polycyclic aromatic hydrocarbons, hydrocarbons, etc., were either fully decomposed or exhibited significant decreases in concentration during the full-scale AOAO process, which offered insights to the biodegradation dynamics of CWW organic components. Microbial community analysis showed that bacterial communities were remarkably altered in the four bioreactors of the AOAO process: Proteobacteria dominated during the whole AOAO process, while Nitrospirae and Bacteroidetes enriched in the primary and secondary AO process, respectively. Moreover, metagenomic sequencing found that the relative abundances of amino acid metabolism and carbohydrate metabolism in the primary AO process were both higher than that in the secondary AO process. It indicated that as the AOAO process progressed, the changes in operational characteristics could remarkably affect the variations of functional microorganisms responsible for organics and nitrogen removal and metabolic functions of microbial community. Through this study, a comprehensive assessment of the AOAO biological processes of coking wastewater treatment was achieved, which provided valuable insights to the operation and evaluation of relevant real treatment plants.